Conventionally, in order to reduce power consumption of a light source and to prolong a life of the device, technology is known for controlling luminance-adjusting values of the light source and correction parameter of display content correlating with each other according to inputted display signals or values measured by a photo sensor, a temperature sensor, or the like, thereby realizing power saving, and a long life.
Document 1 (Published Japanese patent application no. H11-65531) can be cited as one of conventional documents relating to such art.
The invention recited in Document 1 relates to a control method for mainly handling moving pictures. No matter whether or not a display content is updated, always, the characteristic amount of the display content is extracted, and the correction parameter of the display content and the luminance-adjusting value of a light source are all the time renewed based on the extracted characteristic amount.
Especially, in a case where a still picture is displayed, the display content has not been changed for a number of frames. Even in such a case, characteristic amounts are extracted, the correction parameter of display contents and luminance-adjusting values of the light source are kept being renewed. Considerable electric power is consumed by such unnecessary processing.
Electronic devices mainly used for displaying still pictures, have often display resolution higher than that of electronic devices for mainly displaying moving pictures. Therefore, the higher display resolution the electronic devices have, the heavier the burden according to the above-mentioned unnecessary processing is.
Especially, in an electronic device for mainly displaying still pictures, for example an electronic book, a display content is kept not be updated, while a user thereof reads the display content of the displayed pages. Therefore, unnecessary processing regarding some hundreds or thousands of frames is carried out, and considerable electric power is wastefully consumed.    [Document 1] Published Japanese patent application no. H11-65531